Growing herbicide resistance and concerns regarding the environmental and health impacts of synthetic herbicides have intensified interest in plant-derived weed-management products. This review assesses the phytotoxic, herbicidal, and allelopathic potential of essential oils, emphasizing efficacy, selectivity, formulation, and delivery. Relevant literature was identified through searches of Scopus, Web of Science, and Google Scholar, using terms related to essential oils, phytotoxicity, allelopathy, herbicidal activity, and weed management, followed by critical comparison of selected studies. Essential oils from diverse aromatic plants inhibited weed germination and growth through mechanisms including membrane disruption, pigment degradation, oxidative imbalance, and altered antioxidant activity. Species- and genus-specific evidence highlights the considerable chemical diversity of essential oils and identifies numerous compounds and formulation strategies with potential for bioherbicide development. Activity varied according to chemical composition, concentration, formulation, application conditions, and target species. Nanoemulsions, nanocapsules, and cyclodextrin-based systems have been investigated to improve stability, controlled release, and delivery, although improved formulation properties do not necessarily translate into greater herbicidal efficacy. Although some formulations achieved substantial weed suppression with limited crop injury, reported cytogenotoxicity, effects on soil microbial activity, and phytotoxicity at high concentrations highlight the need for further evaluation of potential non-target effects. The available evidence is still dominated by laboratory studies, while field-scale validation remains limited. Essential-oil-based bioherbicides are promising components of integrated weed management, but their practical development requires standardized formulations, mechanistic studies, field-scale validation, economic assessment, regulatory support, and comprehensive evaluation of crop and environmental safety.